Fluid supply failure protection valve

ABSTRACT

A water supply failure protection valve is connected to hot and cold water supplies. The failure protection valve is responsive to the loss of cold water supply pressure to shut off all water flow. The failure protection valve is responsive to the loss of hot water supply pressure to permit cold water flow through both a cold water flow path and a hot water flow path so as to ensure a substantial flow of water to a downstream fixture. The supply failure protection valve may be integrated with a thermal mixing valve to provide water at a preselected temperature.

BACKGROUND OF THE INVENTION

This invention relates generally to a fluid supply failure protectionvalve and more particularly to a protection valve which safelyaccommodates failure of either a hot or a cold water supply to atempering valve.

Tempered fluid mixing systems are used in a variety of commercial and/orindustrial applications, for example, in emergency fixtures such asdrench shower stations and/or safety eyewash stations, which are used torinse hazardous chemicals from a person's skin and clothing or toextinguish burning clothing on a person. A typical system includes athermostatic mixing valve or tempering valve which automatically blendshot and cold water supply streams to produce a mixed, tempered wateroutput stream having a selected temperature, for example about 27degrees C. (80 degrees F.).

A known problem with such tempered water mixing systems is that eitherthe hot or cold water supplies may fail. If the cold water supply fails,the mixing valve will supply potentially scalding hot water to the user,causing the risk of burns and further injury. If the hot water supplyfails, it is possible to continue using the emergency fixture. However,in this case, only cold water will be supplied to the thermostaticmixing valve, which will cause it to restrict the water flow to a levelthat is inadequate for proper rinsing or fire extinguishing. Attemptshave been made in the prior art to provide for the cut-off of hot waterflow in case of a cold water failure, and to provide a bypass flow ofcold water should the hot water supply fail. However, these prior artsystems require either that the tempering valve be replaced with atempering valve of an entirely different design, for both tempering thewater and accommodating the supply failure, or they require that aseparate cold water bypass circuit be plumbed into the system.Accordingly, there is a need for fluid supply failure protection valvewhich protects a fluid system from failure of both hot and cold watersupplies, and which may be integrated into existing systems.

BRIEF SUMMARY OF THE INVENTION

Therefore, it is an object of the invention to provide a fluid supplyfailure protection valve which provides an adequate flow under allpossible conditions.

It is another object of the invention to provide a fluid supply failureprotection valve which may be simply retrofitted into existing temperedfluid supply systems.

It is another object of the invention to provide a fluid supply failureprotection valve which is responsive to a loss of cold fluid supplypressure to shut off all fluid flow.

It is another object of the invention to provide a fluid supply failureprotection valve which is responsive to a loss of hot fluid supplypressure to provide a substantial flow of cold fluid through both hotand cold fluid flow paths.

These and other objects of the present invention are achieved in thepreferred embodiments disclosed below by providing a supply failureprotection valve which includes a housing defining a first fluid inletin fluid communication with a spaced-apart first fluid port, and asecond fluid inlet in fluid communication with a spaced-apart secondfluid port. First valve means permit flow communication between thefirst fluid inlet and the first fluid port in the presence of fluidpressure in the second fluid inlet, and prevent communication betweenthe first fluid inlet and the first fluid port in response to an absenceof fluid pressure in the second fluid inlet. Second valve means forpreventing the flow of fluid from the second fluid inlet to the firstfluid port in the presence of fluid pressure in the first fluid inlet,and for permitting flow communication from the second fluid inlet toboth of the first and second fluid ports in response to the absence ofsupply pressure in the first fluid inlet.

In another embodiment of the present invention, the first valve meansincludes a hollow, open-ended valve sleeve disposed in a bore formed inthe housing, the bore being in fluid communication with the first andsecond fluid inlets. The valve sleeve is movable between a firstposition wherein flow from the first fluid inlet to the first fluid portis permitted, and a second position wherein flow from the first fluidinlet to the first fluid port is blocked.

In another embodiment of the present invention, the second valve meansincludes a piston disposed inside the valve sleeve. The piston ismovable between a closed position wherein flow from the second fluidinlet to the first fluid port is blocked, and an open position whereinflow from the first fluid inlet to the second fluid port is permitted.

In another embodiment of the present invention, the supply failureprotection valve includes first biasing means for urging the valvesleeve towards the first position.

In another embodiment of the present invention, the supply failureprotection valve includes second biasing means for urging the pistontowards the closed position.

In another embodiment of the present invention, the supply failureprotection valve includes a first check valve disposed in the firstfluid inlet. The first check valve allows flow from the first fluidinlet to the bore but prevents flow in the opposite direction.

In another embodiment of the present invention, the supply failureprotection valve includes a second check valve disposed in the secondfluid port. The second check valve allows flow from the bore to thesecond fluid port but prevents flow in the opposite direction.

In another embodiment of the present invention, a fluid supply failureprotection valve includes: a housing having a bore with upper and lowerportions formed therein; a cold fluid inlet for receiving a fluid at afirst temperature, and a hot fluid inlet for receiving a fluid at asecond temperature greater than the first temperature. The hot fluidinlet has a hot fluid check valve disposed therein which allows flowfrom the hot fluid inlet to the bore but prevents flow in the oppositedirection. A hot fluid port is spaced-apart from the hot fluid inlet andconnected in flow communication with the hot fluid inlet. A cold fluidport is spaced-apart from the cold fluid inlet and connected in flowcommunication with the cold fluid inlet. A hollow sleeve disposed in thebore, the sleeve having open upper and lower ends, and a plurality ofside ports formed through the lateral surfaces thereof, the side portsforming a transverse flow path through the sleeve. The sleeve is movablebetween a first position which permits flow communication between thehot fluid inlet and the hot fluid port, and a second position in whichflow communication between the hot fluid inlet and the hot fluid port isblocked;

-   -   an upper biasing means is disposed in the bore above the sleeve,        so as to urge the sleeve towards the first position. A piston is        disposed in the sleeve, and is movable between a closed position        in which the flow of fluid from the cold fluid inlet to the hot        fluid port is blocked, and an open position in which flow        communication is permitted from the cold fluid inlet to both of        the hot and cold fluid ports. A lower biasing means is disposed        in the sleeve between the lower end of the sleeve and the lower        face of the piston, and urges the piston towards the open        position.

The sleeve moves to the first position in the presence of fluid pressurein the cold fluid inlet, and moves to the second position in absence offluid pressure in the cold fluid inlet, and the piston moves to theclosed position in the presence of fluid pressure in the hot fluidinlet, and moves to the open position in response to the absence offluid pressure in the hot fluid inlet.

In another embodiment of the present invention, the supply failureprotection valve includes a cold fluid check valve disposed in the coldfluid port which allows flow from the bore to the cold fluid port butprevents flow in the opposite direction.

In another embodiment of the present invention, the supply failureprotection valve has an upper face carrying an upper seal, a lower facecarrying a lower seal, and a narrow central member connecting the upperand lower faces.

In another embodiment of the present invention, the upper biasing meansincludes a coil spring.

In another embodiment of the present invention, the lower biasing meansincludes a coil spring.

In another embodiment of the present invention, the upper biasing meanscomprises a surface area at the upper end of the sleeve which is greaterthan an opposing surface area at the lower end of the sleeve.

In another embodiment of the present invention, the supply failureprotection valve includes a bypass passage providing flow communicationbetween the hot fluid inlet upstream of the hot fluid check valve andthe lower portion of the bore.

In another embodiment of the present invention, a valve assembly forreceiving hot and cold water streams and providing a mixed output streamat a preselected temperature includes a tempering valve, having: ahousing defining a cold fluid port, a hot fluid port, an outlet port, acold fluid inlet for receiving a fluid at a first temperature, a hotfluid inlet for receiving a fluid at a second temperature greater thanthe first temperature, a first bore and a second bore having upper andlower portions, wherein the hot fluid inlet has a hot fluid check valvedisposed therein which allows flow from the hot fluid inlet to thesecond bore but prevents flow in the opposite direction. A cylinder isdisposed in the first bore in fluid communication with the cold fluidport, the hot fluid port, and the outlet port, the cylinder having upperand lower sealing edges and a cylinder seal which prevents fluidcommunication between the hot and cold water ports.

A temperature-responsive element is connected to the cylinder and isoperative to move the cylinder so as to control the relative proportionsof flow from the hot and cold water ports to the outlet port formaintaining a preselected fluid temperature. A fluid supply failureprotection valve includes: a hollow sleeve disposed in the second bore,the sleeve having open upper and lower ends, and a plurality of sideports formed through the lateral surfaces thereof, the side portsforming a transverse flow path through the sleeve, the sleeve movablebetween a first position which permits flow communication between thehot fluid inlet and the hot fluid port, and a second position in whichflow communication between the hot fluid inlet and the hot fluid port isblocked.

An upper biasing means is disposed in the bore above the sleeve, so asto urge the sleeve towards the first position. A piston is disposed inthe sleeve, the piston movable between a closed position in which theflow of fluid from the cold fluid inlet to the hot fluid port is blockedand an open position in which flow communication is permitted from thecold fluid inlet to both of the hot and cold fluid ports. A lowerbiasing means is disposed in the sleeve between the lower end of thesleeve and the lower face of the piston, the spring urging the pistontowards the open position.

The sleeve moves to the first position in the presence of fluid pressurein the cold fluid inlet, and moves to the second position in absence offluid pressure in the cold fluid inlet, and the piston moves to theclosed position in the presence of fluid pressure in the hot fluidinlet, and moves to the open position in response to the absence offluid pressure in the hot fluid inlet.

In another embodiment of the present invention, the valve assemblyincludes a cold fluid check valve disposed in the cold fluid port whichallows flow from the bore to the cold fluid port but prevents flow inthe opposite direction.

In another embodiment of the present invention, the valve assemblyincludes a movable adjusting stem disposed in the housing which contactsthe temperature-responsive element at a preselected position.

In another embodiment of the present invention, the piston has an upperface carrying an upper seal, a lower face carrying a lower seal, and anarrow central member connecting the upper and lower faces.

The present invention and its advantages over the prior art will becomeapparent upon reading the following detailed description and theappended claims with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention may be best understood by reference to the followingdescription taken in conjunction with the accompanying drawing figuresin which:

FIG. 1 is a cross-sectional view of an exemplary tempering valveincluding a supply failure protection valve constructed in accordancewith the present invention, during a normal operating condition;

FIG. 2 is a view of the valve of FIG. 1, during a condition in which thehot fluid supply has failed;

FIG. 3 is a view of the valve of FIG. 1, during a condition in which thecold fluid supply has failed; and

FIG. 4 is a cross-sectional view of an alternative embodiment of thesupply failure protection valve.

DETAILED DESCRIPTION OF THE INVENTION

Referring to the drawings wherein identical reference numerals denotethe same elements throughout the various views, FIG. 1 illustrates anexemplary fluid supply failure protection valve 10 constructed inaccordance with the present invention. It should be noted that thepresent invention is equally applicable to systems which handle fluidsother than water, and therefore the terms “water” and “fluid” are usedinterchangeably herein when describing the invention. In thisembodiment, the supply failure protection valve 10 is combined with aknown type of tempering valve 12 in a common housing 14. The temperingvalve 12 includes a hot fluid port 16, a cold fluid port 18, and anoutlet port 20. A hollow cylinder 22 with circumferential upper andlower sealing edges 24 and 26 is disposed in a first bore 28 in fluidcommunication with the hot water, cold water, and outlet ports 16, 18,and 20. A cylinder seal 30 prevents leakage between the hot and coldwater ports 16 and 18. A temperature-responsive element 32 is locatedinside the cylinder 22 and connected to the cylinder 22 by acircumferential array of struts 34. For illustrative clarity only onesuch strut 34 is shown in FIGS. 1, 2, and 3. In this example thetemperature-responsive element 32 is a known type of thermomechanicalunit such as a sealed, wax-filled capsule having upper and lower ends 36and 38. However, any other type of device capable of moving the cylinder22 in response to a temperature change may be used. A return spring 40is disposed between the lower end 38 of the temperature-responsiveelement 32 and a seat 42 located at the bottom of the first bore 28. Athreaded adjusting stem 44 is mounted in the housing 14, for example ina removable adjuster cap 46. The adjusting stem 44 is hollow and has anovertravel spring 48 disposed therein. The overtravel spring 48 is heldin by a flat disk 50 and a retaining ring 52 at its lower end.

The tempering valve 12 operates as follows: Water flows into thetempering valve 12 through both the hot and cold ports 16 and 18. Itflows past the upper and lower sealing edges 24 and 26 of the cylinder22, past the temperature-responsive element 32, and through the outletport 20. At temperatures below a selected metering range, the cylinder22 is urged upward by the return spring 40 so that the upper sealingedge 24 contacts an upper sealing surface 54. Therefore, most of theflow of water will be from the hot fluid port 16, past the lower sealingedge 26, and into the outlet port 20. As the temperature increases, thetemperature-responsive element 32 expands upward until a pin 56protruding from the upper end 36 of the temperature-responsive element32 contacts the disk 50. Further expansion of the temperature-responsiveelement 32 causes it to displace the cylinder 22 downward, opening aflow path between the upper sealing edge 24 and the upper sealingsurface 54, simultaneously reducing the size of the flow path beneaththe lower sealing edge 26. As the temperature further increases, thecylinder is finally moved all the way to its lowest position in whichthe lower sealing edge 26 contacts a lower sealing surface 58, thuscutting off all hot water flow. The temperature of the mixed water canbe selected by moving the adjusting screw 44 up or down, which changesthe distance the pin 56 must move before it contacts the disk 50. Undernormal operation, the disk 50 does not move, However, if the temperingvalve 12 should be heated beyond its intended operating range, theexcess force generated by the temperature-responsive element 32 willdisplace the disk 50 and compress the overtravel spring 48. Thisprevents damage to the temperature-responsive element 32.

The failure protection valve 10 includes a second bore 60 formed in thehousing 14. The upper portion 62 of the second bore 60 is in fluidcommunication with the cold fluid port 18 and a cold fluid inlet 64,while the lower portion 66 of the second bore 60 is in fluidcommunication with the hot fluid port 16 and a hot fluid inlet 68. Acold fluid check valve 70 is disposed in the cold fluid port 18 andallows flow to pass from the second bore 60 to the cold fluid port 18,but prevents flow in the opposite direction. A hot fluid check valve 72is disposed in the hot fluid inlet 68 and allows flow to pass from thehot fluid inlet 68 to the second bore 60 but prevents flow in theopposite direction.

A cylindrical, hollow valve sleeve 74 having open upper and lower ends76 and 78 slides in the second bore 60, sealed by first and secondsleeve seals 80 and 82, such as O-rings of a known type. Acircumferential array of side ports 84 are formed in the lateralsurfaces of the valve sleeve 74 near its upper end 76 and define atransverse flow path through the valve sleeve 74. The valve sleeve 74 isbiased downward by an upper bias means 86, which in this case is shownas a spring which is retained by a threaded spring cap 88. The upperbias means 86 may also take the form of an unbalanced surface areaincorporated into the sleeve 74, as described more fully below withrespect to the alternative embodiment shown in FIG. 4A piston 90 isdisposed in the interior of the valve sleeve 74. The piston 90 has anupper face 92 with an upper seal 94, and a lower face 96 with a lowerseal 98. The upper and lower faces 92 and 96 are connected by a narrowcentral member 100. A lower bias spring 102 is disposed in the valvesleeve 74 and extends between the lower face 96 of the piston 90 and aretainer 104 having an opening 106 formed therein. The piston 90 isurged upwards by the lower bias spring 102 so that the upper seal 94seals against a ledge 108 in the valve sleeve 74.

FIG. 1 depicts the operation of the supply failure protection valve 10during normal operation, that is, when both the hot and cold watersupplies (denoted “H” and “C” respectively in FIG. 1) are operating.Cold water from the cold water supply C passes through the cold fluidinlet 64, passes through the second bore 60, into the cold fluid port18, thorough the cold fluid check valve 70, and finally into thetempering valve 12. Hot water from the hot water supply H passes throughthe hot fluid inlet 68. Some of the hot water flow passes through thehot fluid check valve 72, through the side ports 84, around the centralmember 100 of the piston 90, through the hot fluid port 16, and into thetempering valve 12. Optionally, some of the hot water flow from the hotfluid inlet 68 is diverted, before it passes through the hot fluid checkvalve 72, into a bypass passage 110. This bypass flow acts on the bottomend 78 of the valve sleeve 74 and on the lower face 96 of the piston 90.Alternatively, if the bypass passage 110 is not used, a flow path fromthe hot water inlet 68 to the bottom end 78 of the valve sleeve 74 andthe lower face 96 of the piston 90 may be created by eliminating thelower seal 98 and the second sleeve seal 82. In either arrangement,because the supply pressures of the hot and cold water are approximatelyequal, the pressure of the hot water plus the preload of the lower biasspring 102 will keep the piston 90 sealed in its upper (or closed)position and prevent the leakage of cold water into the hot water flowpath, while the pressure of the cold water plus the load of the upperbias means 86 will keep the sleeve 74 seated in its lower position,where it permits hot water to flow from the hot fluid inlet 68 to thehot fluid port 16.

FIG. 2 shows the operation of the supply failure protection valve 10 ina condition where the hot water supply H has failed. In the absence ofthe supply failure protection valve 10, tempering valve 12 would stillbe supplied with cold water through the normal cold water flowpath whenthe hot water supply fails. However, the cold water would besubstantially below the temperature set point of the tempering valve 12,and this would cause the tempering valve to greatly restrict the flow ofcold water, to a level insufficient to provide adequate flow for adownstream fixture.

In contrast, in the supply failure protection valve 10, when the hotwater supply H fails, the pressure on the lower face 96 of the piston 90is relieved. The pressure on the upper face 92 of the piston 90 issufficient to compress the lower bias spring 102 and push the piston 90down to an open position so that the upper seal 94 is unseated and aflowpath is open from the cold fluid inlet 64, downwards through thesecond bore 60, and through the hot fluid port 16 into the temperingvalve 12. If the bypass passage 110 is present, it provides a flowpathfrom the interior of the valve sleeve 74 to the hot fluid inlet 68 (nowat zero pressure) upstream of the hot fluid check valve 72. This allowsany residual hot water which may be contained in the lower end 78 of thevalve sleeve 74 to be expelled so the piston 90 can move down asintended. In the absence of the bypass passage 110, the lower seal 98and the second sleeve seal 82 may be eliminated as described above,which allows any residual hot water to simply flow out between thesleeve 74 and the second bore 60, in turn permitting the piston 90 tomove down.

In this position, cold water flows to the tempering valve 12 throughboth the hot fluid port 16 and the cold fluid port 18. The hot fluidcheck valve 72 prevents cold water from backing up into the hot waterinlet 68. Thus, no matter what the position of the tempering valvecylinder 22, an adequate flow of cold water will flow out of the outletport 20.

FIG. 3 shows the operation of the supply failure protection valve 10 ina condition where the cold water supply C has failed. In this case, thepressure on the upper face 92 of the piston 90 and the upper end 76 ofthe valve sleeve 74 falls to zero. The hot water pressure acting on thelower face 96 of the piston 90 and the lower end 78 of the valve sleeve74 will force the valve sleeve 74 upward, overcoming the upper biasmeans 86. In this position, the side ports 84 are no longer exposed, andthe valve sleeve 74 blocks off flow from the hot fluid inlet 68 to thehot fluid port 16. The cold fluid check valve 70 keeps any residual hotwater pressure from backing up through the cold water port into the coldwater supply C before the hot water flow is fully shut off. In thisposition, no water can flow through the tempering valve 12. Therefore,any chance of scalding is prevented.

FIG. 4 shows an alternative embodiment 210 of the supply failureprotection valve. The supply failure protection valve 210 issubstantially similar to the supply failure protection valve 10described above. It differs in that the supply failure protection valve210 is contained in its own individual housing 214, and is not combinedwith a tempering valve. A central bore 260 is formed in the housing 214.The upper portion 262 of the central bore 260 is in fluid communicationwith a cold fluid port 218 and a cold fluid inlet 264, and is closed offby a cap 288, while the lower portion 266 of the central bore 260 is influid communication with a hot fluid port 216 and a hot fluid inlet 268.A cold fluid check valve 270 is disposed in the cold fluid port 218 andallows flow to pass from the central bore 260 to the cold fluid port218, but prevents flow in the opposite direction. A hot fluid checkvalve 272 is disposed in the hot fluid inlet 268 and allows flow to passfrom the hot fluid inlet 268 to the central bore 260 but prevents flowin the opposite direction.

A hollow cylindrical valve sleeve 274 having open upper and lower ends276 and 278 slides in the central bore 260, sealed by upper and lowersleeve seals 280 and 282, such as the illustrated O-rings. A pluralityof side ports 284 are formed in the lateral surfaces of the valve sleeve274 near its center. The valve sleeve 274 is biased downward by upperbias means 286. In the illustrated embodiment, the upper bias means areimplemented by providing an increased surface area at the upper end 276of the sleeve 274 relative to the opposing surface area at the lower end278 of the sleeve 274. This ensures that here is a net downward force onthe sleeve 274 when the hot and cold water supplies are at the samepressure. A spring such as that illustrated in FIG. 1 (not shown in FIG.4) could also be used to provide an upper biasing means 286. A piston290 is disposed in the interior of the valve sleeve 274. The piston 290has an upper face 292 with an upper seal 294, and a lower face 296 witha lower seal 298, connected by a narrow central member 300. A lower biasspring 302 is disposed in the valve sleeve 274 and extends between thelower face 296 of the piston 290 and a retainer 304 having an opening306 formed therein. The piston 290 is urged upwards by the lower biasspring 302 so that the upper seal 294 seals against a ledge 308 in thevalve sleeve 274. A bypass passage 310 may be used to connect the lowerportion 266 of the bore 260 to the hot fluid inlet 268 upstream of thehot fluid check valve 272. Alternatively, if the bypass passage 310 isnot present, the lower seal 298 and the lower sleeve seal 282 may beeliminated to provide a flow path between the hot fluid inlet 268 andthe lower portion of the bore 266.

The operation of the supply failure protection valve 210 issubstantially the same as that of the supply failure protection valve 10described above. It is installed into a water supply system byconnecting the hot and cold fluid inlets 268 and 264 to hot and coldwater supplies “H” and “C” respectively. The hot and cold water ports216 and 218 are then connected to the hot and cold water inlets of atempering valve (not shown) such as that described above. Thus, it maybe retrofitted into an existing system to provide protection in theevent either supply fails. Alternatively, the supply failure protectionvalve 210 may by connected to a system having a manual mixing valve, orseparate hot and cold water faucets.

The foregoing has described a water supply failure protection valve.While specific embodiments of the present invention have been described,it will be apparent to those skilled in the art that variousmodifications thereto can be made without departing from the spirit andscope of the invention. Accordingly, the foregoing description of thepreferred embodiment of the invention and the best mode for practicingthe invention are provided for the purpose of illustration only and notfor the purpose of limitation, the invention being defined by theclaims.

1. A valve assembly for receiving hot and cold water streams andproviding a mixed output stream at a preselected temperature,comprising: a tempering valve, comprising: a housing defining a coldfluid port, a hot fluid port, an outlet port, a cold fluid inlet forreceiving a fluid at a first temperature, a hot fluid inlet forreceiving a fluid at a second temperature greater than said firsttemperature, a first bore, and a second bore having upper and lowerportions, wherein said hot fluid inlet has a hot fluid check valvedisposed therein which allows flow from said hot fluid inlet to saidsecond bore but prevents flow in the opposite direction; a cylinderdisposed in said first bore in fluid communication with said cold fluidport, said hot fluid port, and said outlet port, said cylinder havingupper and lower sealing edges and a cylinder seal which prevents fluidcommunication between said hot and cold water ports; atemperature-responsive element connected to said cylinder and operativeto move said cylinder so as to control the relative proportions of flowfrom said hot and cold water ports to said outlet port for maintaining apreselected fluid temperature; a fluid supply failure protection valve,comprising: a hollow sleeve disposed in said second bore, said sleevehaving open upper and lower ends, and a plurality of side ports formedthrough the lateral surfaces thereof, said side ports forming atransverse flow path through said sleeve, said sleeve movable between afirst position which permits flow communication between said hot fluidinlet and said hot fluid port, and a second position in which flowcommunication between said hot fluid inlet and said hot fluid port isblocked; an upper biasing means disposed in said second bore above saidsleeve, so as to urge said sleeve towards said first position; a pistondisposed in said sleeve, said piston movable between a closed positionin which the flow of fluid from said cold fluid inlet to said hot fluidport is blocked and an open position in which flow communication ispermitted from said cold fluid inlet to both of said hot and cold fluidports; a lower biasing means disposed in said sleeve between said lowerend of said sleeve and said lower face of said piston, said lowerbiasing means urging said piston towards said open position, wherein:said sleeve moves to said first position in the presence of fluidpressure in said cold fluid inlet, and moves to said second position inabsence of fluid pressure in said cold fluid inlet; and said pistonmoves to said closed position in the presence of fluid pressure in saidhot fluid inlet, and moves to said open position in response to theabsence of fluid pressure in said hot fluid inlet.
 2. The valve assemblyof claim 1 further comprising a cold fluid check valve disposed in saidcold fluid port which allows flow from said bore to said cold fluid portbut prevents flow in the opposite direction.
 3. The valve assembly ofclaim 1 further comprising a movable adjusting stem disposed in saidhousing which contacts said temperature-responsive element at apreselected position.
 4. The valve assembly of claim 1 wherein saidpiston has an upper face carrying an upper seal, a lower face carrying alower seal, and a narrow central member connecting said upper and lowerfaces.
 5. The valve assembly of claim 4 wherein said upper biasing meansincludes a coil spring.
 6. The valve assembly of claim 4 wherein saidupper biasing means comprises a surface area at said upper end of saidsleeve which is greater than an opposing surface area at said lower endof said sleeve.
 7. The valve assembly of claim 4 wherein said lowerbiasing means includes a coil spring.